Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

544
FXUS63 KLOT 271145
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
645 AM CDT Mon Apr 27 2026

.KEY MESSAGES...

- There is a low (10 to 20%) chance of damaging non-thunderstorm
  wind gusts today north of I-80 between noon and 3 PM.

- There is a threat for severe weather today, primarily between
  4 and 11 PM this evening. The main threats are damaging winds
  and damaging hail.

- A transition toward a cooler and drier pattern will commence
  by midweek.

&&

.DISCUSSION...
Issued at 247 AM CDT Mon Apr 27 2026

Early morning radar, satellite, and ASOS/AWOS observations
depict a developing surface low in far southwestern Kansas with
an associated broad warm frontal zone extending eastward through
central Missouri and into far western Tennessee. Broad
southwesterly flow continues to advect an EML plume across the
central Plains, which with a developing low-level jet (some
50-60kt per regional VWPs) and the approach an unbalanced
upper-level short-wavelengh trough propagating into the
Southern Plains, is supporting an expansive region of elevated
gravity wave associated convection (GWAC) across central Kansas
at press time.

Owing to continued synoptic-scale ascent facilitated by the
developing surface low and upper-level trough as well as a steady
northeasterly feed of instability through the night, the expectation
is for the ongoing elevated convection across central Kansas to
coalesce into a bore-driven mesoscale convective system over the
coming hours. The orientation of the low-level jet and instability
axis would then guide the convective system through Kansas City,
Missouri by daybreak and into central Illinois (along/south of I-80)
by mid to late morning. With instability decreasing with eastward
extent, the convective system should begin to weaken as it crosses
the I-39 corridor in central Illinois. With that said, northeasterly-
oriented deep-layer shear vectors will promote a broad stratiform
precipitation region (perhaps with embedded thunder) on the northern
side of the zone of active convection across northern
Illinois/southern Wisconsin. The severe weather threat with the
first batch of activity is currently thought to be low (call it a 5
to 15% chance at any given point) owing to meager instability. With
that said, locally damaging winds cannot be ruled out particularly
south of I-80 with any decaying convective element.

Outside the convection this morning, do have growing concern
for a period of non-thunderstorm damaging winds mainly
along/north of I-80 between noon and 3 PM along the backside of
the decaying stratiform region this afternoon. CAM guidance has
remained remarkably consistent in depicting rapid
drying/subsidence along the backside of the stratiform region,
which would support the development of a very tight pressure
gradient behind the leading meso-high (a wake-low situation). The
HRRR has long had the signal for nearly 24 hours now, including
explicit wind gust output up to 75 mph in the most recent iteration.
It`s always tough to go all-in on these sorts of features given
inherent dependencies on how convection evolves and a history of
false alarms of such by CAM guidance. With that said, will give a
very hearty warning to the incoming day shift to keep an eye out for
even the slightest signs of wake low development to get lead time on
what would probably be a short- fused High Wind Warning.

Attention then turns to the threat for severe weather this
afternoon and evening. There is excellent agreement among
deterministic and ensemble guidance that the upper-level
shortwave currently propagating into the Central Plains will
lift into the Great Lakes region this afternoon, allowing the
aforementioned surface low to track from roughly Kansas City, MO
this morning to near La Crosse, Wisconsin this evening. As the
upper-level wave passes overhead, an associated 75kt 500mb speed
max will arc directly across the Mississippi River as pressure
falls in the central Great Lakes induce the rapid
intensification of the 925- to 850mb wind field. The kinematic
environment will thus become very supportive of organized
convection by this evening.

Meanwhile, increasing isentropic ascent atop the (what will be
outflow-reinforced) warm front will set the stage for festering
convection from eastern Missouri into central Illinois during
the afternoon hours. Even with increasing synoptic southwesterly
flow, a steady feed of cool outflow from the festering
convection will likely impede the northeastward progression of
the warm front, and hence, instability, into area area by early
evening. Heavy cloud cover throughout the day will also hamper
the ability for low-level lapse rates to steepen and surface
temperatures to warm, with highs only poised to make it into the
upper 60s to perhaps locally 70. Nevertheless, cooling mid-
level temperatures (by virtue of synoptic-scale ascent and the
continued advection of an EML plume via southwesterly mid-level
flow) will nevertheless support the development of elevated
instability throughout the afternoon.

Even with a lack of surface-based instability, we still do
expect the rapid development and expansion of convection across
our area this afternoon as the arrival of the upper-level
shortwave interacts with the elevated instability axis.
Accordingly, we continue to see a threat for severe weather this
afternoon and evening in our local area mainly in the form of
locally damaging winds and hail. The inability for the surface-
based instability axis to make it into our area should relegate
the (what will be a higher-end) tornado threat south of our area
across central and southern Illinois, but tracking the exact
location of the warm front will be important in case it does
sneak into our area. So, today still looks active, just not
necessarily what initially looked like a very concerning
scenario in our local area. In collaboration with SPC, the Level
3/5 threat area has been adjusted southward to be closer to the
expected position of the outflow-reinforce warm front this
afternoon.

In spite of the most likely outcome outlined above, do still
feel the need to discuss the low-probability scenario in which
the surface-based instability does make it into our area.
Should convection across central Nebraska fail to coalesce into
a bore-driven MCS (as it has struggled to do so thus far and
instead remain as GWAC), or the convective footprint into
central Illinois is minimized by early afternoon (so no outflow
to counteract southwesterly flow), the safeguard of festering
convection limiting the northeastward-movement of the warm
front would fail to materialize. In such a scenario, the warm
front would be able to lift into at least northwestern Illinois,
leading to a narrow zone where surface-based instability would
overlap with an intense kinematic environment. Should this
occur, a band of supercells with a threat for all hazards
including tornadoes would materialize near the Mississippi River
with upscale growth into an intense squall line thereafter.
Would have to think that instability would still decrease with
eastward extent toward Lake Michigan... though there would still
a more pronounced threat for an all-hazard severe weather
event. Most guidance does not support this outcome at this point
in time, though it does remain completely realistic provided a
lot of dominoes fall in the wrong direction.


Tuesday onward:

The upper-level pattern will undergo a substantial pattern
shift through the rest of the week with predominant aggregate
troughing along the US/Canadian border. As a result, the
expectation is for cooler and drier conditions to prevail with
highs in the 60s and overnight lows in the upper 30s to lower
40s. We can easily envision a threat for frost by the weekend.
Thereafter, long-range ensembles advertise warming trend during
the first week of May.

Borchardt

&&

.AVIATION /12Z TAFS THROUGH 18Z TUESDAY/...
Issued at 645 AM CDT Mon Apr 27 2026

Forecast concerns include...

Chance of thunderstorms late this morning.
Strong/gusty southeast winds today.
Southeast winds gusting 40+ kt possible for 1-2 hr early PM.
Chance of thunderstorms late afternoon thru mid evening.

Isolated showers have developed in an arc from RFD to IKK and
will likely move across the terminals over the next hour. Opted
to include vicinity shower mention with the expected short
duration. A large area of showers and embedded thunder across
southern IA and far northern MO is expected to continue moving
east/northeast across the terminals later this morning. There
remains quite a bit of uncertainty for thunder coverage, which
may remain isolated. Included prob thunder with the 09z update
and maintained thunder mention with the current forecast. The
heaviest thunderstorms and perhaps a broken line of storms is
expected to pass south of the terminals.

Southeast winds will steadily increase this morning with gusts
into the 30kt range expected by late morning and through the
afternoon. Wind directions will turn southerly late this
afternoon, southwest this evening and then westerly overnight
with gusts diminishing into the lower/mid 20kt range. However,
the short term guidance has been consistently showing very
strong winds for 1-2 hours behind the midday showers/isolated
thunderstorms, roughly during the 17z-20z time period. If these
winds materialize as the models are depicting, there could be
southeast winds gusting into the 40-45kt range, possibly higher.
Confidence is low but opted to include a tempo for higher winds,
which may need to be increased further as trends emerge.

While additional thunderstorms are expected to develop this
afternoon, confidence is decreasing for how widespread they will
be over the terminals. The bulk of new thunderstorm development
is expected to be south of the terminals. Made no changes to the
previous vicinity/tempo thunder for late this afternoon into
this evening, but changes are possible with later forecasts.

While low mvfr cigs will be possible with thunderstorms later
this afternoon/evening, prevailing mvfr cigs are expected to
develop overnight and persist through mid/late Tuesday morning.
cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 10 AM CDT Tuesday for the IL
     nearshore waters.

     Small Craft Advisory from 10 AM this morning to 10 AM CDT
     Tuesday for the IN nearshore waters.

&&

$$

Visit us at weather.gov/chicago